Metal ferrite catalyst activation with a large amount of halogen

ABSTRACT

A partially deactivated metal ferrite oxidative dehydrogenation catalyst can be reactivated by contacting the catalyst with a relatively large amount of halogen. For example the yield from a Mg ferrite used in the oxidative dehydrogenation of n-butenes to butadiene had declined from 55.1 to 52.4 percent after 1,350 hours on stream. The catalyst was treated with up to 6,800 ppm of chlorine and after termination of the halogen and removal of residual halogen the yield was 55.9 percent. It was not necessary to remove the catalyst for activation or to stop the oxidative dehydrogenation.

United States Patent Koslosk Jr. [451 Ma 30 1972 1 METAL FERRITECATALYST 3,303,237 2/1967 Croce et a1. ..260/680 E ACTIVATION I A LARGE3,450,788 6/1969 Kehl ....260/683 R 3,526,675 10/1970 Croce et 31...260/680 E [72] Inventor: Frank Koslosky, Jr., Pasadena, Tex. PrimaryExaminerPatrick P. Garvin Assistant ExaminerP. E. Konopka [73] Assignee:getro-TexT Chemical Corporation, A"omey G Baxter Dunaway ouston, ex. 22Filed: June 1, 1970 [57] ABSTRACT A partially deactivated metal ferriteoxidative dehydrogena- [21 1 App! 42553 tion catalyst can be reactivatedby contacting the catalyst with a relatively large amount of halogen.For example the yield 52 U.S. c1 .252/415, 252 470, 252 471, from 8 sferrite used in the exidative dehydrogenation of 252/472 252/473 260/680E butenes to butadiene had declined from 55.1 to 52.4 percent [51] IntCl B0" 11/22 11/64 CO7: after 1,350 hours on stream. The catalyst wastreated with up 58 n 252F115 i 1 1 47o 474 to 6,800 ppm of chlorine andafter termination of the halogen 1 e o are and removal of residualhalogen the yield was 55.9 percent. It 260/680 680 E was not necessaryto remove the catalyst for activation or to f stop the oxidativedehydrogenation. [56] Re erences Cited 8 Claims, No Drawings UNITEDSTATES PATENTS 3,567,793 3/1971 Coiling et al ..252/47l METAL FERRITECATALYST ACTIVATION WITH A LARGE AMOUNT OF HALOGEN The present inventionrelates to the oxidative dehydrogenation of organic compounds in vaporphase over metal ferrite catalysts, more particularly the inventionrelates to a method of activating the metal ferrite catalysts bycontacting the catalysts with a halogen.

Oxidative dehydrogenations employing ferrite catalysts are well known.U.S. Pat. Nos. 3,270,080; 3,284,536; 3,303,234; 3,303,235; 3,303,236;3,303,238; 3,308,182; 3,324,195; 3,334,152; 3,342,890, 3,398,100;3,450,787; 3,420,911; 3,420,912; 3,428,703 and 3,440,299 disclose suchprocesses.

Small quantities of halogens have been added in prior art processes forthereaction of organic compounds in vapor phase at elevated temperature,e.g. to promote cracking (U.S. Pat. No. 2,714,085) to promote oxidation(U.S. Pat. No. 2,480,971) to promote hydrogenation (U.S. Pat. No.1,898,966) and the like.

Recently it has been known to oxidatively dehydrogenate organiccompounds by contacting the organic compounds at elevated temperaturewith oxygen and halogen in the presence of metal ferrite catalysts asshown in U.S. Pat. Nos. 3,270,080; 3,303,234; 3,303,235; 3,303,236;3,303,238; 3,308,182; 3,308,200; 3,334,152 and 3,342,890.

The metal ferrite catalysts have generally been found to be excellentoxidative dehydrogenation catalysts, however, as with most catalysts,they tend to decline in catalytic activity throughout their use, acharacteristic often referred to as time trend. Ultimately the catalyticactivity declines to a point where the catalyst can no longer beeconomically used. At present the catalyst is removed and disposed of.The catalyst represents one of the key cost factors in oxidativedehydrogenations and furthermore disposal of spent catalyst presents anever increasing problem and cost in itself. Thus, if there were a way toreactivate the metal ferrite catalyst, preferably without removing themfrom the reactor, there would be a substantial economic benefit.

It is an object of the present invention to provide a method ofactivating metal ferrite catalyst for use in oxidative dehydrogenations.It is a further object to provide a method of reactivating a spent metalferrite catalyst for use in oxidative dehydrogenations. Another objectis to provide increased yields of the desired products of oxidativedehydrogenation by activating the metal ferrite catalyst. Another objectis to prolong the useful life of the metal ferrite oxidativedehydrogenation catalysts.

These and other objects will become apparent from the followingdescription.

Briefly stated, the present invention is a method of activating a metalferrite oxidative dehydrogenation catalyst comprising contacting saidmetal ferrite with a gas comprising a halogen selected from the groupconsisting of chlorine, bromine, iodine and mixtures thereof or amixture of said halogen with a gas selected from the group consisting ofa reducing gas, inert gas and mixtures thereof, provided that saidmixture contains at least 2,000 ppm of said halogen.

Improved catalytic activity can be obtained by contacting a reduced orunreduced metal ferrite with only a halogen selected from the groupconsisting of chlorine, bromine, iodine and mixtures thereof or in amixture with an inert gas. A suitable inert gas is nitrogen or helium,for example. The quantity of halogen present will be from at least 2,000ppm up to 100 mole percent based on total gases present. Smallquantities of reducing or oxidizing may be present, i.e., up to 10 molepercent of the total gases.

in one embodiment a fresh metal ferrite is activated prior to use in thepresence of a reducing gas which will generally be present in asubstantial quantity. The halogen will be present at 2,000 ppm up toabout 5 weight percent based on the reducing gas. In a further aspect ofthis embodiment the reducing gas is an organic compound which isundergoing oxidatively dehydrogenation. The duration of the contactingwill vary generally between and 72 hours depending on conditions,catalyst, concentration of reactants, etc., however, longer periods canbe employed, for example 7 days or more.

One aspect of the present invention is a method of increasing thecatalytic activity of a metal ferrite oxidative dehydrogenation catalystcomprising (a) contacting in vapor phase in the presence of a reducinggas at least 2,000 ppm based on said reducing gas of a halogen selectedfrom the group consisting of chlorine, bromine, iodine and mixturesthereof, with said metal ferrite oxidative dehydrogenation catalyst, and(b) reducing the amount of said halogen contacting said metal ferriteoxidative dehydrogenation catalyst to less than 2,000 ppm based on saidreducing gas.

When the metal ferrite catalyst to be activated or reactivated (theprocess and effect are the same in either event) is a reduced catalyst,the reduction is usually achieved by contacting the ferrite with areducing gas, for example, hydrogen, CO or a hydrocarbon that is capableof oxidation under the conditions of the contacting. In one embodimentof the present invention the reduction is achieved by the process ofoxidative dehydrogenation in which the catalyst is employed. Generallythe reduction is obtained at a temperature of at least 250 C. with thetemperature of reduction being no greater than 900 C. Where thereduction is carried out independent of the oxidative dehydrogenationthe temperature is usually no greater than 850 C.

A further embodiment relates to the activation of a metal ferriteoxidation catalyst that has been in continuous use for several monthsand whose activity is beginning to decline. The oxidativedehydrogenation can be terminated and the catalyst activated by treatingin halogen alone, halogen in an inert gas or halogen in a reducing gas.The reactivation can take place in the reactor or the catalyst can beconveniently removed to other equipment for the particular purpose ofhalogen activation. The present process, however, can be carried outadvantageously without interruption of the oxidative dehydrogenationprocess by adding at least 2,000 ppm of the halogen up to about 5 weightpercent based on the organic compound to be dehydrogenated for arelatively short duration, e.g. about 10 hours to 72 hours. During thehalogen addition the selectivity of the reaction may drop and thusproduce a reduction in yield. This is a temporary phenomenon and theselectivity and yield will rise after the halogen addition has ceasedand remain at a higher level than prior to the halogen activation.

The halogen present in the dehydrogenation zone may be either elementalhalogen or any compound of halogen which would liberate halogen underthe conditions of reaction. Suitable sources of halogen are such ashydrogen iodide, hydrogen bromide and hydrogen chloride; aliphatichalides, such as ethyl iodide, methyl bromide, methyl chloride, 1,2-dibromo ethane, cycloaliphatic halides, ammonium iodide, ammoniumbromide; ammonium chloride, sulfuryl chloride; metal halides includingmolten halides; and the like. The halogen may be liberated partially orentirely by a solid source as disclosed in the process of U.S. Pat. No.3,130,241 issued Apr. 21, 1964. Mixtures of various sources of halogenmay be used. The amounts of halogen given herein are calculated aselemental halogen.

It has been known prior to this time that the addition of criticalamounts of halogen can give increased catalyst activity. However, theincrease in catalytic activity was related to a continuing halogenpresence. The use of halogen continually in an oxidative dehydrogenationmay be undesirable because of the damage that the halogen may cause whenit contacts metal and other material in the reactor and recoveryequipment, particularly in the presence of water. The relativelyinfrequent use of halogen for short periods of time that the presentprocess requires does not subject the equipment to acid attack to thedegree that continuous treatment does and for that reason is anacceptable expedient for improving catalyst activity.

The present activation can also be used in processes employing acontinuous halogen presence to obtain improved metal ferrite catalystactivity. In such an embodiment the addition of halogen to provide for2,000 ppm to 5 weight percent of halogen based on organic compound to bedehydrogenated may also result in a temporary decline in yield from thereaction, however, after reduction in the halogen to below 2,000 ppmbased on organic compound to be dehydrogenated or to the originalhalogen level improved results will be obtained because of catalystactivation.

The metal ferrite catalysts contain iron, oxygen and at least one othermetallic element Me. The catalysts comprise crystalline compositions oriron, oxygen, and at least one other metallic element Me. The catalystscomprise ferrites. Ordinarily, the ionic radius of the second metallicingredient(s) Me is small enough that the oxygen anions are not spreadtoo far apart. That is, the elements must be able to form a crystallinestructure with the iron and oxygen.

A preferred type of catalyst of this type is that having a facecenteredcubic form of crystalline structure. Examples of this typeof catalystare ferrites of the general formula Moo-Fe where Me is a divalent metalcation such as Mg or Ni. However, if the cations are large, such as Sr(1.35A.), the spine! structure may not occur and other types of ferriteshavinga hexagonal crystal of the type SrO-6Fe O may be formed. Thesehexagonal ferrites are within the scope of the definition of catalystsof this invention.

Suitable catalysts may also be ferrites wherein other metals arepartially substituted for the iron. For example, atoms having a valenceof +3 may be partially substituted for some of the Fe atoms. Also, metalatoms having a valence of +4 may replace some of the Fe*** ions.However, the catalysts will still suitably have iron present in anamount described above in relation to the total atoms of the secondmetallic ingredient(s).

The catalyst may have the iron combined in crystalline structure withoxygen and more than one other metallic element, as mentioned above. Forexample, a preferred type of ferrite is that essentially orapproximately of the formula,

MeFe O where Me represents a divalent metal ion with an ionic radius aroximately between 0.5 and 1.1A., preferably between about 0.6 and 1.0A.in the case of simple ferrites, Me may be, e.g., one of the divalentions of the transition elements as Mg, Ca, Sr. Ba, Cr, Mn, Co, Ni, Zn,or Cd; however, a combination of these ions is also possible to form aferrite such as Ni Mg. Fe 0, or Ni -,Mg .-,,Fe O,. Moreover, the symbolMe may represent a combination of ions which have an average valency oftwo. However, it is essential that the crystalline structure containiron and the metallic element other than iron. I

Examples of catalysts are such as ferrites containing iron combined withat least one element selected from the group consisting of Mg, Zn, Ni,Co, Mn, Cu, Cd, Ca, Ba, Sr, Al, Cr, Ti, V, Mo, W, Na, Li, K, Sn, Pb, Sb,Bi, Ga, Ce, La, Th, other rare earth elements and mixtures thereof, witha preferred group being Mg, Ca, Sr, Ba, Mn, Cr, Co, Ni, Zn, Cd, andmixtures thereof, and particularly preferred metals being Mg or Mn, suchas magnesium ferrite, cobalt ferrite, nickel ferrite, zinc ferrite,barium ferrite, strontium ferrite, manganese ferrite, calcium ferritecadmium ferrite, silver ferrite, zirconium ferrite, and rare earthferrites such as cerium ferrite or mixtures of ferrites. Examples ofmixed ferrites are magnesium ferrite plus zinc ferrite, magnesiumferrite plus nickel ferrite, magnesium ferrite plus cobalt ferrite,magnesium ferrite plus nickel ferrite plus zinc ferrite and magnesiumferrite plus man ganese ferrite. As explained above, these ferrites maybe physical mixtures of the ferrites or may contain crystals wherein thedifferent metallic atoms are contained in the same crystal, or acombination of physical mixtures and chemical combinations. Someexamples of a chemical combination would be magnesium zinc ferrite,magnesium chromium ferrite, zinc chromium ferrite and lanthanum chromiumferrite.

The valency of the metals in the catalysts do not have to be anyparticular values, although certain combinations are preferred asdisclosed elsewhere. The determination of the valency of the ions issometimes difiicult and the results are uncertain. The different ionsmay exist in more than one valency state. However, a preferred catalystis one which has the iron predominately in the Fe*** state. Someferrites are described in Ferromagnetism, by Richard M. Bozorth (D. VanNostrand Co., Inc., 1951), which disclosure is hereby incorporated byreference.

Although the catalysts may be broadly defined as containing crystallinestructures of iron, oxygen and the second metallic ingredient(s),certain types of catalysts are preferred. Valuable catalysts wereproduced comprising as the main active constituent in the catalystsurface exposed to the reaction gases, iron, oxygen and at least oneelement selected from the group of Mn, or Periodic Table Groups 11A, 11Bor Vlll such as those selected from the group consisting of magnesium,manganese, calcium, cadmium, cobalt, zinc, nickel, barium, strontium,and mixtures thereof. The Periodic Table referred to is the one on pages400-401 of the Handbook of Chemistry and Physics (39th edition, 1957-58,Chemical Rubber Publishing Co., Cleveland, Ohio.) Preferred catalystshave iron present as the predominant metal in the catalyst exposed inthe reaction gases.

in one class of catalysts containing two second metallic ingredients arethose of the basic formula Me Cr Fe O, where a can vary within the rangeof about 0.1 to about 3, b can vary from greater than 0 to less than 2and c can vary from greater than 0 to less than 3. Me can be any of themetallic ingredients, other than chromium, previously described,particularly Periodic Table Groups [1A, [13, Ill and Vlll. Inparticularly, the metals from these groups that are desirable are Mg,Ba, La, Ni, Zn, and Cd.

The preferred compositions exhibit a certain type of X-ray diffractionpattern. The preferred compositions do not have any sharp X-raydiffraction reflection peaks as would be found, e.g., in a highlycrystalline material having the same chemical composition. instead, thepreferred compositions of this invention exhibit reflection peaks whichare relatively broad. The degree of sharpness of the reflection peak maybe measured by the reflection peak bank width at half height (W h/2). inother words, the width of the reflection peak as measured at one-half ofthe distance to the top of the peak is the band width at half height."The band width at half height is measured in units of theta. Techniquesfor measuring the band widths are discussed, e.g., in Chapter 9 of Kingand Alexander, X-ray'Difiraction Procedures, John Wiley and Son, N.Y.,1954. The observed band widths at half height of the preferredcompositions of this invention are at least 0.16 2 theta and normallywill be at least 0.20 2 theta.*(*The powder diffraction patterns may bemade, e.g., with a Norelco constant potential diffraction unit type No.1221510 equipped with a wide range goniometer type No. 4227310 cobalttube type No. 32119, proportional counter type No. 5725011; all coupledto the Norelco circuit panel type No. 12206/53. The cobalt K alpharadiation is supplied by operating the tube at a constant potential of30 kilovolts and a current of 10 millamperes. An iron filter is used toremove K beta radiation. The detector voltage is 1,160 volts and thepulse height analyzer is set to accept pulses with amplitudes between 10and 30 volts only. Slits used are divergence 1, receiving 0.006 inch andscatter 1. Strip chart recordings for identification are made with ascanning speed of one-fourth per minute, time constant of 4 seconds anda full scale of 10 counts per second. No correction is made of K adoublet or instrumental broadening of the band widths.) For instance,excellent compositions have been made with band widths at half height ofat least 0.22 or 0.23 2 theta. The particular reflection peak used tomeasure the band width at one half height is the reflection peak havingMiller (hkl) indices of 220. (See, e.g. Chapter of Klug and Alexander,ibid). Applicants do not wish to be limited to any theory of theinvention in regard to the relationship between composition activity andband width.

Suitable preferred ferrites according to this invention are zincferrites having X-ray diffraction peaks within the dspacings 4.83 to4.89, 2.95 to 3.01, 2.51 to 2.57, 2.40 to 2.46, 2.08 to 2.14, 1.69 to1.75, 1.59 to 1.65 and 1.46 to 1.52 with the most intensive peak beingbetween 2.51 to 2.57 manganese ferrite having peaks at d-spacings withinor about 4.87 to 4.93, 2.97 to 3.03, 2.50 to 2.58, 2.09 to 2.15, 1.70 to1.76, 1.61 to 1.67 and 1.47 to 1.53, (with other peaks) with the mostintense peak being between 2.52 to 2.58; magnesium ferrites having peaksbetween 4.80 to 4.86, 2.93 to 2.99, 2.49 to 2.55, 2.06 to 2.12, 1.68 to1.73, 1.58 to 1.63 and 1.45 to 1.50 with the most intense peak beingbetween 2.49 and 2.55; and nickel ferrites having peaks within thed-spacings of 4.79 to 4.85, 2.92 to 2.98, 2.48 to 2.54, 2.05 to 2.11,1.57 to 1.63 and 1.44 to 1.49, with the most intense peak being within2.48 to 2.54. The preferred manganese ferrites are those having the Mnpredominately present as a valence of plus 2.

Ferrite formation may be accomplished by reacting an active compound ofiron with an active compound of the designated metals. By activecompound is meant a compound which is reactive under the conditions toform the ferrite. Starting compounds of iron or the other metal may besuch as the nitrates, hydroxides, hydrates, oxalates, carbonates,acetates, formates, halides, oxides, etc. The starting compounds aresuitably oxides or compounds which will decompose to oxides during theformation of the ferrite such as organic and inorganic salts orhydroxides. For example, manganese carbonate may be reacted with ironoxide hydrates to form manganese ferrite. Salts of the desired metalsmay be coprecipitated and the precipitate heated to form the ferrite.Desired ferrites may be obtained by conducting the reaction to form theferrite at relatively low temperatures, that is, at temperatures lowerthan some of the very high temperatures used for the formation of someof the semiconductor applications. Good results, e.g., have beenobtained by heating the ingredients to a temperature high enough toproduce the required ferrite but at conditions no more severe thanequivalent to heating at 950 C or 1,000 C for 90 minutes in air andgenerally the maximum temperature will be less than l,300 C andpreferably less than 1,150 C. Methods for preparing catalysts suitablefor this invention are disclosed in U.S. Pat. Nos. 3,270,080; 3,248,536;3,303,234-6; 3,303,238; 3,308,182; 3,334,152; 3,342,890 and 3,450,787and these dis closures are hereby incorporated by reference.

The catalysts may contain an excess of iron over the stoichiometricamount to form the ferrite. For example, in a ferrite of the type MeFe Othe stoichiometric amount of iron would be 2 atoms per atom of Me. Theiron (calculated as I e- 0 may be present in an amount of at least about10 percent in excess of the stoichiometric amount and preferably may bepresent in an amount of at least 14 percent in excess. Suitable rangesof iron are from about 10 to 200 percent excess. Similarly the catalystsmay contain an excess of Me over the stoichiometric amount. A suitablerange of Me content would be from about 0.05 to 2 atoms of Me per atomof iron.

The compositions of this invention may also comprise additives, such asdisclosed in U.S. Pat. No. 3,270,080 and U.S. Pat. No. 3,303,238.Phosphorus, silicon, boron, sulfur or mixtures thereof are examples ofadditives. Excellent catalysts may contain less than 5 weight percent,and preferably less than 2 weight percent, of sodium or potassium in thesurface of the catalyst. Solid sulfur containing compounds such asmanganese sulfate can be incorporated along with manganese carbonate toform a sulfur containing manganese ferrite. Another method is to mix aferrite, e.g. nickel ferrite with a solution of sulfuric acid. Theresulting slurry can then be dried and pelleted or coated on a carrierand then dried.

Carriers or supports for the catalyst may be employed such as aluminapumice, silica and so forth. Diluents and binders may also be used.Unless stated otherwise, the compositions referred to in thisapplication are the main active constituents of the dehydrogenationprocess during dehydrogenation and any ratios and percentages refer tothe surface of the catalyst in contact with the gaseous phase duringdehydrogenation.

The process of this invention may be applied to the dehydrogenation of awide variety of organic compounds. Such compounds normally will containfrom two to 20 carbon atoms, at least one II II grouping, a boilingpoint below about 350 C, and such compounds may contain other elements,in addition to carbon and hydrogen such as oxygen, halogens, nitrogenand sulfur. Preferred are compounds having two to 12 carbon atoms, andespecially preferred are compounds of three to six or eight carbonatoms.

Among the types of organic compounds which may be dehydrogenated bymeans of the process of this invention are nitriles, amines, alkylhalides, ethers, esters, aldehydes, ketones, alcohols, acids, alkylaromatic compounds, alkyl heterocyclic compounds, cycloalkanes, alkanes,alkenes, and the like. Illustration of dehydrogenations includepropionitrile to acrylonitrile; propionaldehyde to acrolein; ethylchloride to vinyl chloride; methyl'isobutyrate to methyl methacrylate; 2or 3-chlorobutene-l or 2, 3-dichlorobutane to chloroprene; ethylpyridine to vinyl pyridine; ethylbenzene to styrene; isopropylbenzene toa-methyl styrene; ethylcyclohexane to styrene; cyclohexane to benzene;ethane to ethylene or acetylene; propane to propylene methyl acetylene,allene, or benzene; isobutane to isobutylene; n-butane to butene andbutadiene-1,3; n-butene to butadiene-l,3, and vinyl acetylene; methylbutene to isoprene; cyclopentane to cyclopentene andcyclopentadiene-l,3; n-octane to ethyl benzene and orthoxylene;monomethylheptanes to xylenes; ethyl acetate to vinyl acetate;2,4,4-trimethylpentane to xylenes; and the like. This invention may beuseful for the formation of new carbon to carbon bonds by the removal ofhydrogen atoms such as the formation of a carbocyclic compound from twoaliphatic hydrocarbon compounds or the formation of a dicyclic compoundfrom a monocyclic compound having an acyclic group such as theconversion of propene to diallyl. Representative materials which aredehydrogenated by the novel process of this invention include ethyltoluene, alkyl chloropbenzenes, ethyl napthalene, isobutyronitrile,propyl chloride, isobutyl chloride, ethyl fluoride, ethyl bromide,n-pentyl iodide, ethyl dichloride, 1,3, -dichloropbutane,1,4-dichlorobutane, the chlorofluoroethanes, methyl pentane, methylethylketone, diethyl ketone, n-butyl alcohol, methyl propionate and the like.

Suitable dehydrogenation reactions are the following: Acyclic compoundshaving four to five non-quarternary contiguous carbon atoms to thecorresponding olefins, diolefins or acetylenes having the same number ofcarbon atoms; aliphatic hydrocarbons having six to 16 carbon atoms andat least one quartemary carbon atom to aromatic compounds, such as2,4,4-trimethylpentene-1 to a mixture of xylenes; acyclic compoundshaving six to 16 carbon atoms and no quarternary carbon atoms toaromatic compounds such as n-hexenes to benzene; cycloparafiins andcycloolefins having five to eight carbon atoms to the correspondingolefin, diolefin or aromatic compound, e.g., cyclohexane to cyclohexeneor cyclohexadiene or benzene; aromatic compounds having eight to 12carbon atoms including one or two alkyl side chains of two to threecarbon atoms to the corresponding aromatic with unsaturated side chainssuch as ethyl benzene to styrene.

The preferred compounds to be dehydrogenated are hydrocarbons with aparticular preferred class being acyclic non-quartemary hydrocarbonshaving four to five contiguous carbon atoms or ethyl benzene and thepreferred products are n-butene-l or 2, butadiene-l,3, vinyl acetylene,2-methyl-lbutene, 3-methyl-l-butene, 2-methyl-2-butene, isoprene,styrene or mixtures thereof. Especially preferred as feed are nbutene-lor 2 and the methyl butenes and mixtures thereof such as hydrocarbonmixtures containing these compounds in at least 50 mole percent.

The dehydrogenation reaction may be carried out at atmospheric pressure,superatrnospheric pressure or at sub-atmospheric pressure. The totalpressure of the system will normally be about or in excess ofatmospheric pressure, although sub-atmospheric pressure may alsodesirably be used.

Generally, the total pressure will be between about 4 p.s.i.a. and about100 or 125 p.s.i.a. Preferably, the total pressure will be less thanabout 75 p.s.i.a. and excellent results are obtained at aboutatmospheric pressure.

The organic compound to be dehydrogenated is contacted with oxygen inorder for the oxygen to oxidatively dehydrogenate the compound. Oxygenmay be fed to the reactor as pure oxygen, as air, as oxygen-enrichedair, oxygen mixed with diluents, solid oxidants, and so forth. Oxygenmay also be added in increments to the dehydrogenation zone. Althoughdeterminations regarding the mechanism of reaction are difficult, theprocess of this invention is an oxidative dehydrogenation processwherein the predominant mechanism of this invention is by the reactionof oxygen with the hydrogen released from the hydrocarbon.

The amount of oxygen employed may vary depending upon the desired resultsuch as conversion, selectivity and the number of hydrogen atoms beingremoved. Thus, to dehydrogenate butane to butene requires less oxygenthan if the reaction proceeds to produce butadiene. Normally oxygen willbe supplied (including all sources, e.g. air to the reactor) in thedehydrogenation zone in an amount from about 0.2 to 1.5, preferably 0.3to 1.2 moles per mole of H being, liberated from the organic compound.Ordinarily the moles of oxygen supplied will be in the range of from 0.2to 2.0 moles per mole of organic compound to be dehydrogenated and formost dehydrogenations this will be within the range of 0.25 to 1.5 molesof oxygen per mole of organic compound.

Preferably, the reaction mixture contains a quantity of steam or diluentsuch as nitrogen with the range generally being between about 2 and 40moles of steam per mole of organic compound to be dehydrogenated.Preferably, steam will be present in an amount from about 3 to 35 molesper mole of organic compound to be dehydrogenated and excellent resultshave been obtained within the range of about 5 to about 30 moles ofsteam per mole or organic compound to be dehydrogenated. The functionsof the steam are several-fold, and the steam may not merely act as adiluent. Diluents generally may be used in the same quantities asspecified for the steam. These gases serve also to reduce the partialpressure of the organic compound.

The temperature for the dehydrogenation reaction generally will be atleast about 250 C., such as greater than about 300 or 375 C., and themaximum temperature in the reactor may be about 700 or 800 C., orperhaps higher such as 900 C. under certain circumstances. However,excellent results are obtained within the range of or about 350 to 700C. such as from or about 400 C. to or about 675 C. The temperatures aremeasured at the maximum temperature in the dehydrogenation zone.

The gaseous reactants may be conducted through the reaction chamber at afairly wide range of flow rates. The optimum flow rate will be dependentupon such variables as the temperature of reaction, pressure, particlesize, and so forth. Desirable flow rates may be established by oneskilled in the art. Generally the 110w rates will be within the range ofabout 0.10 to liquid volumes of the organic compound to bedehydrogenated per volume of dehydrogenation zone containing catalystper hour (referred to as LHSV). Usually, the LHSV will be between 0.15and about 5. For calculations, the volume of a fixed bed dehydrogenationzone containing catalyst is that original void volume of reactor spacecontaining catalyst.

The process of this invention utilizes either a fixed bed or moving bed,such as a fluidized catalyst reactor. Reactors which have been used forthe dehydrogenation of hydrocarbons by non-oxidative dehydrogenation aresatisfactory such as the reactors for the dehydrogenation of n-butene tobutadiene-l,3. Although means to remove heat from the reactor may beemployed, such as coils, the invention is particularly useful withessentially adiabatic reactors where heat removal is a problem.

A further advantage of the present process is that the activatinghalogen may be present in addition to process halogen. Generally processhalogen will be present in an amount far less than the 2,000 ppm basedon the weight of or- 5 ganic compound being dehydrogenated required inthe present invention. Preferred ranges of process halogen are less than1,000 ppm with ranges up to 700 or 800 ppm being particularly suitable.Very small quantities are utilized to achieve improvement such as about10 ppm. Optimum ranges are about to 800 ppm and 75 to 700 ppm. Thehalogen can be added continuously, however, it is not essential andincrements of process halogen can be added so that the level of halogenremains within the stated ranges. The sources of halogen are the same aspreviously given.

The following examples will further illustrate the invention. Allpercentages are weight percent unless otherwise indicated. Allconversions, selectivities and yields are expressed in mole percent ofthe designated feed.

EXAMPLES 1-14 These examples demonstrate several of the variousembodiments described above. The process was the oxidativedehydrogenation of n-butenes (90 percent n-butene-2 and nbutene-l, theremainder being n-butane, isobutane and butadiene) to butadiene. TheLHSV was 1.5, the mole ratio of steam to hydrocarbon was 15 and the moleratio'of oxygen to hydrocarbon was 0.55. The reactor employed a inch bedof catalyst with thermodectors located at spaced intervals through thelength of the bed. The temperature profile of the reaction in the bedwas maintained by adjusting the inlet temperature of the incoming gasesas required which varied from 744-807 F. The catalyst was a magnesiumferrite having a weight ratio of Fe O to MgO of about 4.4 to 1 preparedby slurrying Fe O -l-l o, MgCO and 2 weight percent MgCl-ll O. Theslurry was extruded, dried, milled, mixed with a 3 percent solution of85 percent phosphoric acid, discharged into a suitable mill, formed into1% inch pellets, dried and calcined in air for 1 hour at l,590 F.Chlorine was added to the reactor ahead of the catalyst as anhydrousHCl. Other conditions and the results are shown in the Table.

TABLE Results, mole Conditions percent Hours Inlet Max Con- Exon C1,temp temp, ver- Selecample stream p.p.1n F sion tivity Yield 1- 708 7451,118 60. 4 91. 3 55. 1 2 1, 3&9 745 1, 122 57. 8 90. 7 52. 4 3 400 700755 1, 115 65. 8 92. 4 '60. S 4 1, 600 700 755 1, 108 65. 1 93. 0 60. 55 1, 900 200 755 1, 115 66. 1 92. 0 60. 8 6 2, 185 30 755 1, 115 60. 7Q2. 2 55. 0 465 600 757 1, 112 63. 9 9'2. 8 59. 3 2, 766 2, 300 772 1,135 60. 7 90. 9 55. 2 2, 898 3, 500 795 1, 162 61. 5 91. 5 56. 2 3, 0204, 300 800 1, 160 60. 2 92. 3 55. 6 3, 115 4, 300 802 1, 125 61. 4 91. 856. 4 3, 196 6, 800 798 1, 120 61. 0 91. 7 65. 9 3, 427 850 753 1, 10567. 5 93. 3 63. 0 3, 95 753 1, 123 61. 2 91. 3 55. 9

*S/HC mole ratio 18/1.

Example 1 shows the high degree of activity in a fresh catalyst after700 hours on stream. Example 2 shows the decline in catalytic activityof the catalyst after 1,349 hours on fect of small quantities, e.g.,30-700 ppm of a halogen. Examples 8 12 demonstrate the deactiving effectof larger quantities than about 2,000 ppm on the dehydrogenation. Thesuppressing effects of the large amounts of halogen are dispelled whenthe halogen concentration is reduced as shown in Example 13. AlsoExample 13 demonstrates the activing effect of high concentration ofhalogen, (compare the oxidative dehydrogenation in the presence of smallamounts of halogen before and after activation, Examples 37 and 13respective stream. Examples 37 demonstract the known enhancing ef-Example 14 demonstrates the improvement in the catalyst activity in anoxidative dehydrogenation in the absence of any halogen. Example 14 gavea 6.7 percent higher yield than that obtained from the unactivatedcatalyst of Example 2 and a slightly better yield than the freshcatalyst of Example 1. Chromatographic analysis of the product stream ofExample 14 showed no detectable halogen thus assuring that the resultreflected a true activation of the catalyst and not merely the effect ofresidual halogen.

No significance is attached to the low halogen concentration of Examples3-7 other than the previously known promoting effect of halogen on theoxidative dehydrogenation. It has been observed many times that thetermination of halogen, for example, after Example 6 will result in acontinuing decline in the yield as the halogen concentration declinesuntil all of the residual halogen has been removed at which time thecatalyst will have returned to substantially the same degree of activitythat would have resulted from continued use if the low halogenconcentration had never been present, i.e., in this case less than 52.4percent yield.

The invention claimed is:

1. A method of reactivating a preformed metal ferrite catalystdeactivated in the oxidative dehydrogenation of dehydrogenatablehydrocarbon compounds, wherein the metal portion of said metal ferriteis selected from the group consisting of Mg, Ca, Sr, Ba, Mn, Cr, Co, Ni,Zn, Cd and mixtures thereof comprising;

a. contacting said deactivated preformed metal ferrite oxidativedehydrogenation catalyst with a reactivation gas selected from the groupconsisting of a hydrocarbon gas, an inert gas and mixtures thereofcontaining from 2,000 parts per million to about 5 weight percent basedon the weight of said gas of a halogen selected from the groupconsisting of chlorine, bromine, iodine and mixtures thereof at atemperature of about 250 to 900 C. and at an LHSV ofabout 0.10 to l0.and

b. terminating said halogen addition in about 10 hours to 7 days.

2. The method of claim 1 wherein the reactivation gas is a hydrocarbongas additionally containing 0.2 to 2.0 moles of oxygen per mole ofhydrocarbon.

3. The method according to claim 1 wherein the hydrocarbon compound tobe dehydrogenated contains two to 20 carbon atoms.

4. The method according to claim 1 wherein the metal is Mg or Mn.

5. The method according to claim 4 wherein the metal is Mg.

6. The method according to claim 5 wherein the halogen is chlorine.

7. The method according to claim 6 wherein the hydrocarbon compound tobe dehydrogenated is an acyclic non-quartemary hydrocarbon having fourto five contiguous carbon atoms.

8. The method according to claim 7 wherein the hydrocarbon is a normalbutene.

2. The method of claim 1 wherein the reactivation gas is a hydrocarbongas additionally containing 0.2 to 2.0 moles of oxygen per mole ofhydrocarbon.
 3. The method according to claim 1 wherein the hydrocarboncompound to be dehydrogenated contains two to 20 carbon atoms.
 4. Themethod according to claim 1 wherein the metal is Mg or Mn.
 5. The methodaccording to claim 4 wherein the metal is Mg.
 6. The method according toclaim 5 wherein the halogen is chlorine.
 7. The method according toclaim 6 wherein the hydrocarbon compound to be dehydrogenated is anacyclic non-quarternary hydrocarbon having four to five contiguouscarbon atoms.
 8. The method according to claim 7 wherein the hydrocarbonis a normal butene.